Process of recovering salts formed in the manufacture of artificial silk



UNITED STATES PATENT OFFICE.

EMILE BRONNER'I, OF MIILHAUSEN, ALSAGE-L ORRAINE, FRANCE.

PROCESS OF BECOVERING SALTS FORMED IN THE MANUFACTURE OF ARTIFICIALPatented May 3, 1921.

' SILK.

1 37 71 Specification of Letters Patent.

No Drawing.

T 0 all whom it may concern:

Be it known that I, EMILE BRONNERT, a citizen of the Republic of France,residing at l Quai du Barrage, in Miilhausen, Alsace- Lorraine', France,have invented certain new and useful Improvements in Processes ofRecovering Salts Formed in the Manufacture of Artificial Silk, of whichthe following is a specification.

This invention relates to the production of artificial silk and itsobject is to provide a process for the suitable recovery of a spinningbath from the salts formed by the spinning of viscose in sulfuric acidmixed with soluble sulfates.

It has already been proposed to recover the Glauber salt or sulfate ofsoda from the sulfuric acid baths used with admixture of salt forspinning, viscose. Practically this recovery has not yet been carriedout in any artificial silk factory of the world, at least not to anyconsiderable or useful extent; on the contrary the washing watercontaining the Glauber salt has all been allowed to run to waste and sofar not utilized.

Recently, however, on again taking up the wholesale production of thespecial line of artificial silk known as staple fiber, the idea wasagain entertained of the utilization of the salts contained in thespinning baths, and a practical solution of the problem was sought.

Now it has been found that from the spinning baths properly so-calledthe sodium sulfate formed is recoverable with difficulty. For example,in spinning baths of strong salt content and the usual content ofsulfuric acid exceeding the bisulfate proportion, almost e v'bole quntity of sodium sulfate forms-{l remains adherent to the threads arisingfrom the ath with the usual speed of about 45 m. per minute.

A portion of the salt may undoubtedly be recovered by allowing itssolution to drip off the spools or reels or by shaking it off thethreads. The major portion, however, can only be recovered by subsequentlixiviation of the threads and the diluted wash water must then besteamed with the expenditure of coal and then caused to crystallize,sometimes by additional cooling. The salt thus crystallized outmust thenbe removed and be separated from the acid mother lye by lixiviation.

The free acid still present in the wash Application filed September 7,1920. Serial No. 408,690.

water can be neutralized by the addition of caustic soda or soda, so asto permit ordina riy pans of iron or silicon iron to be used.

hen attempts were made to reduce the quantity of wash water bylixiviation of the raw, slightly acid thread masses with limitedquantities of water and by repeated wash-.

ing with the same water. On using baths of strong salt content it wasfound that, upon the addition of 3 liters of water per hour, or thefirst wash water upon the masses of thread (about 3 kg. dry weight) afurther enrichment is no longer possible after the wash water has beenonce used owing to the occurrence of a compensatory condition of about18 to 20% sodium sulfate and 34% acid in the wash water and upon thethread. In cold weather the tendency for crystallization of the Glaubersalt is also manifest in an unpleasant manner, namely by stopping up ofthe pipes. Finally care must be taken not to begin too soon with the useof the fresh threads as otherwise prior to the complete coagulation andneutralization of the soda the threads only stick or adhere together.

Now it has been found that there can be recovered from the thread massesa far greater quantity of salt if, at the beginning, not pure water butdiluted sulfuric acid is used for the lixiviation, the content of thesolution in acid being sufficient to change the sulfate contained-inthe-threads into the much more easily soluble bisulfate. This does notchoke the pipes. A 10 to 12% acid is preferable, but I am not bound tothis concentration. The concentration must be adapted to the bathconcentrations used at the time.

The greatest advantage, however, consists in the fact that the workingup of these concentrated solutions is extremely simple and advantageous.

Consideration of the matter will show that it would be quite contrary tothe purpose in view to attempt to produce Glauber salt,- either for saleor for reuse in the spinning bath by dissolving the Glauber salt insulfuric acid. To render the Glauber salt in condition for sale afurther purification would be necessary either by crystallizing or byfiltration of the solutions for the removal of adherent quantities ofsulfur from the spinning bath.

A quantity of fresh. sulfuric acid must always be suppliedto theexisting bath, in

the same proportion .as this is weakened by the caustic soda from theviscose and furthermore sulfate as a substitute for that carried awaymust be added; thus the production of bisulfate or of a concentratedbisulfate solution, even also containing excess acid under certaincircumstances, is the most suitable method of recuperation of the sodiumsulfate formed upon the threads.

The corresponding sulfuric acid washing waters are concentrated insuitable manner, as, for example, in steam heated lead pans, in sulfuricacid concentrating towers, wherein hot gases of combustion meet thetrickling bisulfate solution, or by means of other devices, in a stateto be directly run back to the spinning bath, and used therein withoutother alteration of its concentration, as the concentrating in. theconcentration apparatus may be carried out so as to reduce the astrength to the normal or standard used in the baths, or withinpermissible approximations of such standards.

The lixiviation of the thread masses and liberation as far as ossiblefrom the washing liquid can be e ected according to the most variedprocesses, either in vats with circulating liquors and subsequentpressing v erable importance,

' salts formed.

formed in the spinning bath I otash arising possesses still more thanlauber salt the unpleasant property of crystallizing. Hence when workingwith potash combinations the use of the processdescribed is ,preminentlyuseful as potassium bisulfate is just as easily soluble. Because of thehigh commercial value of potash, the reduction in thepotashlosses is ofconsid- Magnesium and zinc salts, which often serve as an addition tospinning baths, do not effect my process for the recovery of the What I'claimis l 1. The process of recovering the salts formed in themanufacture of artificial silk consisting in lixiviating the threadswith dilute sulfuric acid to convertthe salts into salts of a moresoluble character.- V y 2. The process of recovering salts formed insulfuric acid recipitation baths containing dissolvedsu fates used inthe manufactureof artificial silk from viscose solutions, comprisinglixiviating the threads in sulfuric acid solutionto convertthe sulfatesformed in the precipitating bath into the -bisulfate.

In witness whereof I have hereunto si ned my name in the presence of twosubscri. ing

wltnesses.

" 'ELHLEIBBONFNERT. 7 I

